Why not? One of the reasons dinosaurs are so popular is because we can't see any living ones. Even though they did exist, and fossils tell us a great deal about them, there's still so much we don't know --- and so our imaginations help us fill in the blanks. In the case of cryptozoans and mythological creatures, where there isn't even proof that they ever existed, our imagination has even more play. By attaching the details of actual anatomical structures to imaginary animals, we exercise both our knowledge of real science while taking our imaginations out to play.